Washington and Moscow went eyeball to eyeball Tuesday on who was responsible for downing the Malaysian airliner in Ukraine on July 17 and Washington blinked. “We don't know a name, we don't know a rank and we're not even 100 percent sure of a nationality," a U.S. intelligence official told a select group of reporters on condition that he not be named. "There is not going to be a Perry Mason moment here," the official added.

The briefing, conducted at the headquarters of Director of National Intelligence James Clapper, appeared to undermine much of what the administration had been saying about Russian culpability for the downing of Malaysia Flight 17, which killed all 298 aboard.

Moscow has said that it doesn’t know who shot down the jetliner, but suggested that a Ukrainian fighter jet and even the CIA may have been involved. “I’d like to say that the information we have presented here is based on objective and reliable data from various technical systems – unlike the groundless accusations made against Russia,” a statement by senior Russian military commanders said Tuesday. “For example, media circulated a video supposedly showing a Buk [anti-aircraft missile] system being moved from Ukraine to Russia. This is clearly a fabrication.

“US officials claim they have satellite photographs proving the Malaysian airliner was shot down by a missile launched by the militia,” the statement added. “But no one has seen these photographs so far.”

According to the U.S. intelligence official today, the downing was probably “a mistake” by pro-Russian separatists. “The plane was likely shot down by an SA-11 surface-to-air missile fired by Russian-backed separatists in eastern Ukraine,” the Associated Press said, summarizing the official U.S. view. The official cited electronic “intercepts, satellite photos and social media postings by separatists, some of which have been authenticated by U.S. experts.

“But the officials said they did not know who fired the missile or whether any Russian operatives were present at the missile launch,” the A.P. said. “They were not certain that the missile crew was trained in Russia, although they described a stepped-up campaign in recent weeks by Russia to arm and train the rebels, which they say has continued even after the downing of the commercial jetliner.”

A U.S. intelligence assessment posted by the American embassy in Kiev over the weekend painted a far clearer picture of Russian culpability, citing “an intercepted conversation” in which “a known-separatist leader tells another person that a separatist faction downed the aircraft. After it became evident that the plane was a civilian airliner, separatists deleted social media posts boasting about shooting down a plane and possessing a [Russian made] Buk (SA-11) SAM system.”

Administration officials had long argued that the separatists were creatures of Moscow, largely armed and paid by Russian security forces.

Analysts suspected that the Obama administration backed away from fingering Moscow more directly Tuesday for the shoot-down because it needs Russia’s help in other arenas, in particular Iranian nuclear talks and Syria. “I wonder what Putin told Obama,” said one analyst who is not authorized to speak independently of his organization. “[It was probably,] You want our cooperation on a nuclear deal with Iran? Then shut the fuck up.”

Today’s assessment gives Russian President Vladimir Putin some much-needed breathing room, not just from Washington but from Russian nationalist political pressure for him to be more aggressive on Ukraine in the face of U.S. threats and sanctions.

Dimitri K. Simes, a Russian-born expert on the Kremlin, told Newsweek that Putin “is between a rock and a hard place” on Ukraine. “It’s very difficult for him to find the right political balance between not engaging in a Ukrainian adventure and at the same time not to appear weak to his main Russian nationalist constituency,” Simes said in a telephone interview. “If it looks like he has abandoned Ukraine, and at the same time there are sanctions against Russia which leads to a deterioration of living standards of most Russians, I think that for the first time during his rule he then would become politically vulnerable.”

The main political threat to Putin comes not from dissatisfied oligarchs, whom he can compensate for financial losses from the sanctions, but Russian nationalists, said Simes, who heads the Washington-based, middle of the road think tank The Center for the National Interest.

Having failed to seize eastern Ukraine and under political pressure from the right, Putin “would have a very unattractive choice between becoming even more authoritarian – considerably more authoritarian, not really allowing any criticism, totally controlling not just the TV channels but all the Russian media, putting his opponents in jail, not just when they organize demonstrations and engage in disobedience but simply because they express different opinion,” Simes said. “That’s not the way he has wanted to rule so far, and it would be devastating in terms of attracting foreign investment.”

A coup d’etat, put in motion by nationalist sympathizers in Russia’s security and military services, Simes said, is not unimaginable in the long term, “if there is a combination of him surrendering eastern Ukraine and, simultaneously, a decline in living standards. Then he may become vulnerable to all kinds of conspiracies. They are not there yet, but knowing Putin, I would be surprised if he does not keep this possibility in mind as he decides how to proceed.”

But Andrei Soldatov, a Russian investigative journalist and Russian security services expert, dismissed a right-wing coup scenario. “What they lack is organization,” Soldatov, co-founder of the the Agentura.Ru web site, told Newsweek. “The only one which was important, had been destroyed by the FSB” -- Russia’s internal security bureau -- “a few years ago. So nationalist feelings are strong, but with no organization, it’s unlikely to come to something serious.”

Jeff Stein writes Spytalk from Washington. He can be reached confidentially via spytalk(at)me.com.